This invention relates to torque motors and more particularly to flat armature torque motors of the general kind shown in the U.S. Patents of Gamble, No. 2,718,614 issued Sept. 20, 1955; Atchley, No. 2,891,181 issued June 16, 1959; Duff, No. 3,214,646 issued Oct. 26, 1965; and Hansen et al, No. 3,938,778 issued Feb. 17, 1976.
In flat armature torque motors of the general kind described in the above-identified patents, permanent magnets are mounted on the poles and direct a substantial flux through air gaps between the poles and through the armature member which is normally spring-centered in the gap between the poles. Such torque motors further commonly employ bobbin wound coils by means of which a portion of the magnetic flux may be subtracted at one air gap and added at the opposite air gap for causing the armature to be urged in one or the other direction. The movement of the armature, under the influence of the high magnetic flux and the imbalance of the flux created by the bobbin wound coils is carried usually by direct lever connections to a remote location where a part is caused to be moved by the torque motor.
Such motors are characterized by a relatively high force output compared to a relatively low amount of control current required, and this force, or position output of the armature, may be proportional to a DC current applied to one or the other coils.
Construction of a torque motor requires that two pole members be spaced from each other a finite distance defining the armature or air gap. However, under the influence of the relatively high magnetic force, the poles tend to close this gap or become unbalanced.
Present arrangements for controlling this air gap include the use of wide support brackets at the center of the pole piece with no support at the outer extreme ends where the forces are the greatest. Also, tubular spacers with screws through the spacers have been used at the ends of the pole pieces. However, these arrangements either provide no support at the ends of the pole pieces to control the air gap or require additional parts and machining operations in order to control this air gap. Plus the tubular spacer arrangement requires large ledges on the pole pieces that tend to short circuit the magnetic flux path, or otherwise increase magnetic leakage.